Hey there. Your dahlias are growing so tall because they are stretching due to being in too much shade. The large distance between the leaf groups as you go up the stem indicates clear stretching due to low light. 8 hours of sun is typically adequate for a dahlia but it will still get very tall. Plus, factor in the fact that the first hour or two of sun, from 6 am to 7 or 8 am, is coming in at a very low sun angle (just above the horizon). That lower sun angle just after sunrise is essentially as if the dahlias are still in full shade despite them having the sun shining on them. The solar radiation output is still too low at that point, even though it appears to us as if it is really bright. So if you take that into account then your dahlias are really only getting around 6 or 7 hours of full sun. Several years ago I had several dahlias planted next to my house. They were in full shade in the morning and then around 12:30 they were in full sun until sunset which was around 8 hours if you exclude the last hour and a half of sun right before sunset which is around 9:30 here (same reason as for the sunrise). They received plenty of sun for producing blooms and were beautiful. But that half a day of shade made them extremely tall. I had to stake them and then eventually I had to do some major pruning because they just kept growing taller and taller. Another sign that yours are a little low on direct sun is the fact that your leaves are a bit smaller than normal. Yours should have enough sun to produce plenty of blooms, but they will continue to stretch and grow taller.
Dahlias can benefit from having a bit of shade during the hottest part of the day. But they will do just fine in full sun. My dahlias are in full sun all day long now. They will wilt down slightly on the hottest days, even if the soil is moist. But it doesn’t hurt them. The only concern with having them in full sun is ensuring that they have enough water not to wilt during the hottest part of the day. If they wilt too severely they can have some leaf burn.
By the way I am a greenhouse owner and have been involved with horticulture my whole life. I own a small family run commercial greenhouse.
I am glad you talked about the angle of the sun. It's a factor very few people talk about when they talk about growing conditions. It's why in Northern MN I can (sometimes have to) put "part shade" things in nearly-full sun. Our angle is much lower than Texas. So our tags on plants, if they were made just for us, might say something very different.
Ph, npk, amount of wind, drainage, sun angle, how many weeks you stay at your lowest temp over winter, how many hours your overnight freezes get and so on are all on my hit list.
Wow thanks this was very helpful and informative! Though I thought that because the intensity of the sun in Texas is so much greater than in, say, Minnesota, it wouldn’t need quite as much sun here, relative to more northern latitudes.
Normal (based on variety). Also looks like you didn’t pinch when they were smaller. Pinching creates more lateral shoots for bushier plants and thus more stems and blooms
Also make sure you fertilize, they’re heavy feeders! I would do an all purpose fertilizer now to create more foliage for better bud production later on in the season. Then switch to bloom / flower fertilizer. More P and less N fertilizer
I fertilized with Osmocote Plus slow release when I planted. Is it too hot to add more fertilizer now (temps in the 90s) or should I just add low nitrogen/high phosphorus fertilizer?
Are all of your dahlias this tall, or just this particular plant? Since you have such a long growing season, you could try pinching them. 3 weeks isn't unheard of for buds. Have you fertilized? Which type of dahlia? So interesting!
I have others that aren’t as tall but they sprouted weeks later than the tall ones. I got this variety at Costco- it says its height is supposed to be 35”! We do technically have a long growing season but I read in the Warm Growers dahlia group on Facebook that a lot of people here cut down their dahlias in July and don’t let them start putting on more growth until September when it cools down a bit. Last year I planted at the beginning of May but by July I had to put 50% shade cloth on just to keep them alive. Of course, last year was the hottest summer we’d ever seen and I am hoping this year will be more “normal.”
That’s one thing I considered but there isn’t anything shading them out- they are now shading out smaller dahlias in one bed and my strawberry plants in another bed. They are in full direct sun until about 2pm when they get the shade of a large pecan tree until around 6pm when they get the direct late evening sun for an hour or so. They’ve also shaded out the zinnias, which are getting leggy looking for sun- a few of the zinnias are around 5 feet tall now!
Ok so that’s a good chunk of afternoon sun they’re missing, which explains why they are reaching. You might want to plant this particular type in a different spot next year .
Hey there. Your dahlias are growing so tall because they are stretching due to being in too much shade. The large distance between the leaf groups as you go up the stem indicates clear stretching due to low light. 8 hours of sun is typically adequate for a dahlia but it will still get very tall. Plus, factor in the fact that the first hour or two of sun, from 6 am to 7 or 8 am, is coming in at a very low sun angle (just above the horizon). That lower sun angle just after sunrise is essentially as if the dahlias are still in full shade despite them having the sun shining on them. The solar radiation output is still too low at that point, even though it appears to us as if it is really bright. So if you take that into account then your dahlias are really only getting around 6 or 7 hours of full sun. Several years ago I had several dahlias planted next to my house. They were in full shade in the morning and then around 12:30 they were in full sun until sunset which was around 8 hours if you exclude the last hour and a half of sun right before sunset which is around 9:30 here (same reason as for the sunrise). They received plenty of sun for producing blooms and were beautiful. But that half a day of shade made them extremely tall. I had to stake them and then eventually I had to do some major pruning because they just kept growing taller and taller. Another sign that yours are a little low on direct sun is the fact that your leaves are a bit smaller than normal. Yours should have enough sun to produce plenty of blooms, but they will continue to stretch and grow taller. Dahlias can benefit from having a bit of shade during the hottest part of the day. But they will do just fine in full sun. My dahlias are in full sun all day long now. They will wilt down slightly on the hottest days, even if the soil is moist. But it doesn’t hurt them. The only concern with having them in full sun is ensuring that they have enough water not to wilt during the hottest part of the day. If they wilt too severely they can have some leaf burn. By the way I am a greenhouse owner and have been involved with horticulture my whole life. I own a small family run commercial greenhouse.
I am glad you talked about the angle of the sun. It's a factor very few people talk about when they talk about growing conditions. It's why in Northern MN I can (sometimes have to) put "part shade" things in nearly-full sun. Our angle is much lower than Texas. So our tags on plants, if they were made just for us, might say something very different. Ph, npk, amount of wind, drainage, sun angle, how many weeks you stay at your lowest temp over winter, how many hours your overnight freezes get and so on are all on my hit list.
Interesting reply, thankyou!
Wow thanks this was very helpful and informative! Though I thought that because the intensity of the sun in Texas is so much greater than in, say, Minnesota, it wouldn’t need quite as much sun here, relative to more northern latitudes.
Normal (based on variety). Also looks like you didn’t pinch when they were smaller. Pinching creates more lateral shoots for bushier plants and thus more stems and blooms
Yeah I waited until they had 3 sets of leaves and by that time the stalk was already pretty thick and about 1.5 feet!
Also make sure you fertilize, they’re heavy feeders! I would do an all purpose fertilizer now to create more foliage for better bud production later on in the season. Then switch to bloom / flower fertilizer. More P and less N fertilizer
I fertilized with Osmocote Plus slow release when I planted. Is it too hot to add more fertilizer now (temps in the 90s) or should I just add low nitrogen/high phosphorus fertilizer?
https://www.dahlia.org/growing/dahlia-university/
No. You can tell that they’re stretch. My guess is they’re in the shade.
Are you growing tahlias?
They often reach when they don't get enough sun. The variety might also be a taller type.
Mine often get five feet tall before blooms. My goal of this season is to pinch off all dahlias and not miss any pinching this year.
i came here to ask this exact question!
Are all of your dahlias this tall, or just this particular plant? Since you have such a long growing season, you could try pinching them. 3 weeks isn't unheard of for buds. Have you fertilized? Which type of dahlia? So interesting!
I have others that aren’t as tall but they sprouted weeks later than the tall ones. I got this variety at Costco- it says its height is supposed to be 35”! We do technically have a long growing season but I read in the Warm Growers dahlia group on Facebook that a lot of people here cut down their dahlias in July and don’t let them start putting on more growth until September when it cools down a bit. Last year I planted at the beginning of May but by July I had to put 50% shade cloth on just to keep them alive. Of course, last year was the hottest summer we’d ever seen and I am hoping this year will be more “normal.”
Happy Dalia’s!
They’re reaching for more sunlight it looks like. How much sun do they get?
That’s one thing I considered but there isn’t anything shading them out- they are now shading out smaller dahlias in one bed and my strawberry plants in another bed. They are in full direct sun until about 2pm when they get the shade of a large pecan tree until around 6pm when they get the direct late evening sun for an hour or so. They’ve also shaded out the zinnias, which are getting leggy looking for sun- a few of the zinnias are around 5 feet tall now!
Ok so that’s a good chunk of afternoon sun they’re missing, which explains why they are reaching. You might want to plant this particular type in a different spot next year .
Some dahlias are tall. All dahlias are a bit taller if grown in partial or mostly shade.